Interstitial Fluid Balance Resulting from Intestinal‐Hepatic Interaction

Abstract

The anatomical interconnections between the liver and intestines make interstitial fluid balance complex and experimental data exceedingly difficult to interpret. The portal vein connects the intestinal and hepatic blood circulations, and the cisterna chyli connects the intestinal and hepatic lymphatic systems. Furthermore, mathematical models designed to relate interstitial volumes and lymph flows to critical parameters either oversimplify the lymphatic system or overcomplicate the vascular system. Therefore, we developed a model that predicts interstitial pressures and lymph flows by adjusting the relative complexity of the lymphatic and vascular circulations. First, microvascular filtration was characterized by the Starling‐Landis equation. Second, lymphatic flow was made more realistic by assuming it to be more sensitive to inlet than outlet pressure. Third, blood flows were characterized by arterial, venous, and portal resistances. Finally, linearization and judicious use of simplifying assumptions yielded simple, algebraic solutions for interstitial pressures and lymph flows. The resulting model is comprehensive enough to reproduce conditions as diverse as interstitial edema, ascites formation, and changes in lymph flow, resulting from as diverse stimuli as inflammation, portal hypertension, hemodilution, and elevated central venous pressure.